Protein kinases are a broad class of enzymes which act to modify chemically many cellular proteins, by phosphorylation of amino acids.
Inhibitors of protein kinases are structurally varied, and have variable (and sometimes contradictory) effects on the nervous system and other tissues. A given protein kinase inhibitor may influence more than one protein kinase. For example, K-252a, an alkaloid-like material isolated from the culture broth of Nocardiopsis sp. and Actinomadula sp. was originally reported to be a protein kinase C inhibitor, but was subsequently found also to inhibit protein kinases A and G, myosin light-chain kinase, and trk (a tyrosine kinase activated by nerve growth factor [NGF], the latter a neurotrophic protein which promotes the survival of peripheral, sensory and sympathetic neurons).
Consistent with this latter effect, K-252a blocks the neurotrophic actions of NGF on PC-12 cells (chromaffin cells from rat adrenal medullary tumors, pheochromocytomas), and promotes the survival of dorsal root ganglion neurons and hippocampal neurons. However, it has been found to be cytotoxic at a wide range of concentrations, leading some investigators to conclude that it has limited usefulness in vivo.
A microbial alkaloid related to K-252a, staurosporine, also has a variety of effects on different protein kinases and cell types. Staurosporine was found to have NGF-like effects on PC-12 cells, and to protect the gerbil hippocampus from post-ischemic injury. It is able to reverse damage to cholinergic neurons in the rat basal forebrain.
K-252a and staurosporine have been proposed as tumor inhibitors. Staurosporine has been offered as an insecticide. Derivatives of staurosporine, with a hydrocarbyl radical or an acyl radical substituted at the methylamine nitrogen, have been made and proposed for the following uses: tumor inhibition, inflammation inhibition, immunomodulation, and treatment of diseases of the cardiovascular and central nervous systems.